Text by: Anurag Mishra
The term ‘gecko’ might lead one to picture the drab brownish lizards ambling on the walls in homes, occasionally sticking out a tongue to grab insects and then disappearing into any crevice available. However, the leopard geckos, of the family Eublepharidae, are anything but the quintessential picture of the gecko. They are amongst the most peculiar lizards with large-sized bodies and funky colours. They are also the only geckos with movable eyelids and are known for their longevity (most species exceeding 20 years in captivity).
While encounters in the wild are rare, they have been traded as pets as early as the 1960s and are the third most popular reptile in the pet trade. If the laws in one’s country allow, a leopard gecko could even be bought off eBay.
Geckos sourced from the pet trade are also a popular ‘model organism’ in biological research. Model organisms are those that are widely used in laboratory experiments to answer biological questions, ranging from physiology and development to behaviour. An ideal model organism is easy to care for in captivity, reproduces in a short time and is amenable to experimental manipulation. Captive care guidelines, embryonic stage tables and an annotated genome for the leopard gecko are now public resources. However, it is important to ascertain if the source populations used in lab studies represent pure breeding lines to warrant their continued use as model organisms.
With large immovable eyelids, leopard geckos (Eublepharis macularius) are among the most peculiar in the gecko group. Photo: Eduardo_Santos-Eduardo Santos from BH, Brasil, CC BY 2.0 Cover photo: West Indian leopard gecko in Maharashtra. Cover photo: ePhotocorp/Getty Images
While much is known about the organism in captivity, almost nothing is known about the species’ natural history in its native ranges. Its evolutionary history is poorly understood. It is the least diverse of gekkotan families, with just six genera and forty described species. The distribution of different genera in this family is remarkably disjunct: Aeluroscalabotes and Goniurosaurus in East and Southeast Asia; Coleonyx in the southwestern United States, Mexico and Central America; Hemitheconyx and Holodactylus in the arid parts of Africa; and Eublepharis in South and West Asia.
A recent study in Molecular Phylogenetics and Evolution attempts to unravel the evolutionary history of this group at different scales in an integrative manner to answer questions related to evolution and diversification patterns within the group at geological timescales while also seeking clarity on the origins of captive samples. For the study, arising from a collaboration between ten scientists across four countries, the authors generated DNA sequences for Indian species and captive trade samples of Eublepharis for the first time and combined them with data on species from Pakistan, Turkmenistan and Iran to answer these questions.
If these geckos are so popular in the pet trade and laboratories worldwide, why didn’t anyone look into these questions before?
The lead author of this study, Ishan Agarwal, says, “The leopard geckos are not encountered very frequently, meaning, developing a study just to sample for these geckos was not a very feasible idea.” Agarwal has been studying geckos for over a decade now and collected samples of leopard geckos opportunistically on field visits for other projects. During his postdoctoral stint at the National Centre of Biological Sciences (NCBS), Bangalore, enough leopard gecko samples were accumulated to finally ask interesting research questions.
The work initially started with a primary focus on understanding the Eublepharis genus’s diversification within India. The initial results revealed that the Eublepharidae family originated in the Cretaceous period around 77 million years ago (MYA), which means they might have shared space with dinosaurs for a brief while. The first Eublepharid lizards most likely inhabited the Laurasian landmass.
Eublepharis diverged from the African ancestors and dispersed into India after the Indian plate collided with the Eurasian plate somewhere between 35 to 55 MYA, during a period of global warmth.
Eublepharis satpuraensis , a gecko endemic to central Indian states of Madhya Pradesh, Maharashtra and Chhattisgarh, is the most recently described among the Indian lineages. Photo: Ishan Agarwal
Three of the Eublepharis species occur in deciduous forests. The Indian plate was ancestrally forested and wet, and most dry-zone species were considered to have come through recent dispersals. This study, thus, adds to the list of dry zone species with ancient history in India, suggesting arid zones in the Indian subcontinent existed as early as the Oligocene, about 30 million years ago.
The lacertid lizard genus Ophisops has also had a similar pattern of origin in the Saharo-Arabian region and consequent dispersal to India, suggesting arid-zone specialists were able to disperse between these two regions in the late Oligocene, 23-14 MYA.
Agarwal then moved to Vilanova University, U.S., for a second postdoctoral stint, where he collaborated with Tony Gamble and Aaron Bauer, two other leading gecko experts. Their collection of samples from the pet trade was added to the existing ones to expand the scope of the study. Further help from scientists in Slovakia and Pakistan brought the study to its final form.
The Eublepharis genus has divergent lineages in the Eastern Ghats of Peninsular India, Western Himalayas, Pakistan, Rajasthan in Western India all the way up to the western limit in Iran. While some of these distinct lineages have only 2-3% variation genetically within 600-1200 km (E. fuscus, E. macularius and the lineage from the Himalayas), the lineage in Pakistan and E. hardwickii show variations of ~3.5% within just 100-300 km. The highest diversity of species within Eublepharis is in northern Pakistan, where three species are found within just 80 km of each other, at similar altitudes. This region is a tri-junction between the Indus River Basin, Shiwaliks and lower Hindukush mountains, with each lineage associated with one of these geographic features. The authors suggest the complex geography of the region has prevented their interbreeding.
Lastly, data from the pet trade reveals that E. macularius are not exceptionally diverse. These samples are genetically very similar to wild specimens caught from Karachi and the Salt Range, indicating these regions as sources of captive geckos for the pet trade. According to the authors, while they varied considerably in their outer appearance, the genetic homogeneity warrants their continued use as model organisms.
This story was first published in Mongabay India
